BOTH failed "open," at the SAME time, after years of use. That surprised me, because for them to BOTH fail "open" in this Mr. Coffee, they must have failed at EXACTLY the same time
Perhaps they both failed at the same time because they're both in proximity to a heat source that exceeded their rated temperature -- say, when the thermostat failed closed and didn't shut off the warmer? I'd guess both failing open has less to do with some mystery defect in the batch of fuses and more to do with there being a legitimate failure event that tripped them both. Thermal fuses don't blow instantly (it takes a few seconds for the fused bit to melt) so it's quite possible one failed shortly after the other within a few seconds of hitting melting temperature; cutting power doesn't instantly reduce the temperature below that point, so after the first popped and killed the element, the second proceeded to melt anyways and boom, two open thermal fuses.